Wood-boring insects are among the most destructive pests of ornamental trees and shrubs. Most borers are the larvae (immature stages) of certain moths and beetles. The tunnel and feed under the bark in living wood, destroying water- and sap-conducting tissues. This causes girdling, branch dieback, structural weakness, and decline and eventual death of susceptible plants. Infestation sites also provide entry points for plant pathogens.
Clearwing and flathead borers are the main types that attack woody ornamentals. The groups differ somewhat in their habits and host preferences, which can affect the approach for controlling them with insecticides. The keys to controlling these pests are to keep plants healthy and, if necessary, to treat during those times of the year when the insects are vulnerable to insecticides.
Borers rarely infest healthy plants growing in their natural environments. However, when trees or shrubs are transplanted into the landscape, stresses such as drought, soil compaction, sunscald, or injuries can weaken them and make them more susceptible to attack. Adults may locate suitable egg-laying sites by responding to volatile chemicals that emanate from stressed trees.
Adult borers emerge from infested trees in the spring or summer. After mating, the females fly to a suitable host and lay eggs on the bark, often in crevices or around wounds. Hatching occurs about ten days to 2 weeks later. The young larvae quickly tunnel beneath the bark, where they feed and grow. Once inside the tree, borer larvae are no longer vulnerable to insecticide sprays and are seldom detected until serious damage has been done.
Several species of clearwing and flathead borers can infest landscape plants. While some are attracted to a range of hosts, most attack only certain kinds of trees and shrubs. It is important to know when the adults of each species are active and which plants are vulnerable in order for treatment to be effective.
11 Signs That Your Tree Has Disease, Insects, Mites or is Just Downright Unhealthy
Unbeknownst to you, tree and shrub damage may be taking place right under your nose from common culprits like disease, insects, and mites. Oftentimes, these problems can become widespread before you even notice them. That’s because there is a huge variety of shrub and tree insects and diseases that can wreak havoc – and many of them are not very easy to identify. In many cases, the damage has been going on for years until it becomes so severe that it’s obvious.
You probably don’t know how to tell if your tree has a disease or if insects or mites are causing problems, but there are some common signs you can look for which might help you spot a problem early.
While there are dozens of common issues, and we aren’t expecting homeowners to make exact diagnoses, we want to help you spot common problems before they’re too late.
Being armed with some basic diagnostic tools may help you avoid losing a mature plant that you value. It will also help you know when it might be time to call a tree service professional. Here are 11 signs of common tree and shrub problems for you to get familiar with.
Chewed Foliage on Trees & Shrubs
If you notice shrub or tree leaves being eaten, such as small holes or irregular, jagged edges, you could have a variety of different insect problems at hand. This might be an insect larvae, Beetle, or even a weevil issue.
Different insects leave different chewing patterns and sometimes even chew on different parts of the leaf. Beetles, for instance, tend to feast on the middle part of the foliage, skeletonizing the leaves, leaving only the veins. As long as you’re on the lookout for damage, an expert will be able to identify the exact cause and treat it.
Aphids, which are small, soft-bodied insects that tend to multiply quickly, have piercing-sucking mouthparts that they use to feed on plant sap. Some trees are sensitive to the saliva that aphids inject during feeding and may respond by puckering or distorting. This can begin to happen with only a few aphids. Because they can spread rapidly, early detection is key to saving your tree.
Stippled Dull Foliage
A mite infestation can cause foliage to become stippled, yellow, and dry. Mites suck juices from the plants, causing their foliage to become dull and ultimately curl and distort.
Lacebugs and scale insects can have a similar impact. An expert can help determine if your tree is being eaten by insects and exactly what kind of insect it is.
White Spots on Trees & Shrubs
If you see a suspicious abundance of white spots on your twigs, branches, or leaves, you may have an infestation of scale insects, which are parasites of plants and feed on internal plant fluids.
The white spots that you see are, in fact, thousands of tiny white bugs. They are often mistakenly identified by homeowners as mould or parts of the bark. Scale insects can be flat, small 1/16″ long flecks, while others can be larger bumps almost the size of a ladybug, covering smaller twigs.
Cottony White Masses
If you’ve noticed cottony white masses in your trees, it’s possible you have a colony of insects like woolly Aphids, scale or adelgid taking up residence. These pests can be mistaken for fuzzy mould but are actually a type of sucking insect that lives off of plant fluids. Egg sacks from certain insects can also appear as white cottony masses.
Holes in the Bark of Trees & Shrubs
Bark holes, sometimes also accompanied by sawdust coming from these holes, may seem like a telltale sign that your tree being eaten by insects. The common culprit is likely the larvae of wood-boring insect. The flying adult tree borer insects emerge from inside the tree from small exit holes and lay their eggs in cracks of bark or at the base of trees.
When these larvae hatch, they work their way into the tree, tunnelling and boring throughout the layer of the tree immediately behind the bark. This activity interrupts the tree’s vascular system, not allowing water or nutrients to pass borer paths. Eventually, this will cause large sections of the entire tree or shrub to die.
If you’re noticing a black, sooty mould on your landscape plants, what you’re actually seeing is the mould growing on “honeydew,” a substance excreted from certain insects like aphids, whiteflies or scale insects. These insects create this substance after feeding upon plant sugars, and spotting it is a telltale sign that insects are eating your shrub or tree.
Leaf Spots on Tree or Shrub Leaves or Needles
While some white or tan spots are more likely the sign of an insect problem, if you see orange, yellow, black, or brown spotting on your leaves, your tree or shrub may have a form of fungal disease.
Leaf spot diseases can weaken your tree by interrupting its photosynthesis process, ultimately leading to leaf loss. Some diseases can remain cosmetic for the most part, while others mean major health issues for plants.
Yellowing of Foliage
If you’ve witnessed an overall yellowing or even a complete lack of vibrant foliage colour, there are a number of potential culprits. For one, it could simply be caused by either too much or too little moisture. But yellowing can also relate to pest problems, diseases, or even soil fertility.
Stunted Leaf Growth
There are a number of common culprits for leaves that look sickly or small, and it could be related to insects, disease, or other health factors. If you’ve noticed your leaves are not reaching their full potential, it’s worth discussing your concerns with an expert.
Thin or Stunted Trees or Shrubs
Again, plants that are thinner or smaller than they should be can be the result of any one of these issues. It will take an expert assessment to determine what’s holding your trees and shrubs back. If you feel like your trees or shrubs are not looking like they should, it might be time for a more thorough assessment.
How To Prevent And Control Insects On Shrubs And Trees
As with any other organic life form, ornamental shrubs and trees can have problems with insect pests. As human beings who see these critters attack our plants, the question becomes: To kill or not to kill the critters. Sometimes, spraying a broad-spectrum insecticide can actually do more harm than good when beneficial insects are killed in the process. So when we see a bug on our shrub(s), we should first attempt to identify the type of insect and whether or not it is listed as a harmful pest or a beneficial insect.
If you see a ladybug on a leaf, it’s probably busy feasting on and controlling damaging aphid insects naturally. So, as you can see, the identification of an insect can be very important.
Though some insects can do a lot of superficial damage to plants or trees, they usually don’t kill plants. That said, repeated infestations can compromise a plant or tree and leave it susceptible to diseases that can be harmful or deadly.
Many insects are here today and gone tomorrow without doing a bit of harm. The most damaging insects are often the one’s you can’t see; either they are too small (mites), or they’re hiding out on the undersides of leaves (aphids, lace bugs). Others, such as the non-native Japanese Beetle, can hang around for weeks or months, chewing away at foliage and flowers.
If you see an insect on a plant and no apparent damage is done, resist the urge to immediately spray to kill. If you see the damage, it might be time to take control measures. If it’s just a few insects here and there, you can pick or spray them off the plant. For example, at first sight of mealybugs, I usually just spray them off with a blast of water from the garden hose, which usually does the trick. On the other hand, if an infestation occurs, I’ll spray to kill.
When there is an infestation, I use several generally safe products to control harmful insects on most shrubs and trees. When using these products, always follow the instructions on the label.
Note: To avoid harming beneficial insects and pollinators, I always spray in the very early morning or late evening hours, when these beneficial insects are not active. Too, I try to avoid spraying flowers if possible.
Neem Oil. I use this one on ornamental shrubs and trees and in my vegetable garden. Neem oil (azadirachtin) acts as a feeding repellent that can prevent many types of pests and diseases. It also can affect the growth and development of some pests to suppress problems. Susceptibility to neem varies greatly among different insect species, so check the label carefully to ensure that it covers pests you are trying to manage.
Pyrethrin. Products containing pyrethrins are very broad-spectrum insecticides. They attack the nervous system of almost all insects and other arthropods, including spiders and mites. Pyrethrins are very effective as contact sprays but are deactivated quickly by sunlight, moisture, and air, so no residue is left behind.
Sevin / Carbyrl. When it comes to controlling the Japanese Beetle, nothing works better than liquid Sevin spray. Sevin is also effective on many other types of insects listed on the product label, including fleas, ticks and ants.
Malathion. I use this to control whiteflies on gardenias and other plants and lace bugs on azaleas and other plants.
Cyonara Lawn and Garden Insect Control. Cyonara is an excellent professional-grade insect control spray that treats a wide variety of the most common insect pests on shrubs and trees and on lawns, yards, vegetable gardens, roses and flowers. Cyonara is fast-acting on insects with a quick knockdown and offers eight weeks of residual protection.
Fertilome Tree and Shrub Insect Drench. I use this one on crape myrtles, roses, and other plants and trees that I know are always bothered by certain very damaging insect pests. Once this systemic insecticidal drench is applied, it moves down through the soil, where it is absorbed by the roots of the plant or tree. Once absorbed, it moves up through the tree or shrub, providing year-long insect protection. Fertilome Tree & Shrub Insect Drench even move into new growth after application, thus protecting it, too.